Calcium-acidic phospholipid-phosphate complexes have been associated with the initiation of in vitro and in vivo mineralization (e.g., endochondral ossification). The distribution of such complexes in normal (developing dentin, fracture callus) and abnormal calcifications (osteoarthritic osteophytes, necrotic bone, salivary stones) is being studied. Factors which control lipid-induced calcification from solution include pH, Ca and PO4 concentration, the presence of calcification inhibitors, the presence of surfactants (such as the lysophosphatides), and the presence of specific enzymes. The precise role of phospholipase A2, (an enzyme whose activity increases in the epiphyseal growth plate prior to calcification), in lipid induced calcification is being studied by determining the effects of the enzyme on the kinetics of in vitro hydroxyapatite formation. The role of Mg, pH, and other controlling factors is being evaluated in similar kinetic experiments.